Use of prosthetic implants for bone is rapidly increasing in the medical community. Orthopaedic prosthetic implants are commonly made of titanium (Ti) alloy because of its corrosion resistance to body fluids. However, Ti alloys do not form a direct bond with bone. It has been demonstrated that a calcium phosphate coating on the titanium enhances bone apposition to endosseous implants. It is believed that the calcium phosphate permits bone to bond to the coated prosthetic surface and thus enhances implant fixation. Hydroxyapatite (HA) (Ca.sub.5 (PO.sub.4).sub.3 OH) and tricalcium phosphate (TCP) (Ca.sub.3 (PO.sub.4)) are particularly attractive materials for coating titanium for hard tissue implants in plastic surgery because of their capability of directly integrating to bone tissues by their resorption (e.g. TCP) or by facilitating bone bonding of newly forming bone into their structures (e.g. HA). Several methods have been used for applying the coating to the titanium including plasma spraying which is the most frequently used technique to produce HA coatings.sup.1-3. Other, less frequently used methods include solution deposition sometimes referred to as biomimetic process.sup.2,4. Present methods of making TCP or HA coatings result either in very porous coatings (less than 80% of theoretical density) from less than 1 micron to many microns thick, or in dense coatings (greater than or equal to 80% of theoretical density) by deposition of particles (thermo-spray).sup.1 which limits the thickness of the dense coating to be at least 5 micron.
In the technically unrelated field of semiconductor manufacture, plasma-enhanced metalorganic chemical vapor deposition (PEMOCVD) has been used for deposition of ceramic coatings of oxides and nitrides for semiconductor applications. (Calcium phosphate and hydroxyapatite are not used in semiconductor manufacture.) In the PEMOCVD process, a gaseous stream of metalorganic precursors containing the reactive constituents for the desired ceramic (oxide or nitride) coating material and a plasma are directed toward a heated semiconductor substrate, where the plasma ionizes and activates the gaseous stream and a reaction takes place to form a solid film or coating. Reaction byproducts are pumped out. The process is terminated when a desired coating thickness is obtained. PEMOCVD is known to be capable to produce uniform coatings on complex-shape substrates. More specifically, semiconductor manufacture uses PEMOCVD to deposit silicon oxide onto various layers of an electronic chip. PEMOCVD is also used in the semiconductor manufacture to deposit doped gallium arsenide and/or doped gallium nitride onto gallium arsenide or silicon for laser material.
Hence, there is a need in the manufacture of implants for a method of producing a thin and dense implant coating that is less expensive than present coating methods. There may also be a need in optical device manufacture for a method of coating the optical device.